I. Field
The present invention generally relates to optical and electronic devices, systems and methods that include optically sensitive material, such as nanocrystals or other optically sensitive material, and methods of making and using the devices and systems.
II. Background
In image sensors, maximizing signal-to-noise ratio for a given scene, or lighting level, is desired. One means is to maximize signal, such as by maximizing quantum efficiency of the sensor, and by maximizing its fill factor. Minimizing noise includes a number of components, included in which is minimizing noise associated with the process of resetting the level of the storage node associated with each pixel between each frame interval.
An example of the significance of reset noise, also referred to as kT/C noise, is illustrated in FIG. 1 where a column reset introduces kT/C noise, whose charge can dominate over a photodiode in low light. Thermal noise is electronic noise generated by the thermal agitation of charge carriers, such as electrons, in a circuit. The root-mean-square noise voltage, v, generated in a circuit is:v=sqrt(kT/C)where k is Boltzmann's constant in Joules per degree Kelvin, and C is the capacitance value in a circuit. In addition to or as an alternative to calculating voltage noise, the reset noise of capacitive sensors (e.g., image sensors) is often a limiting source of noise. The reset noise can be quantified as the electrical charge, Q, standard deviation:Q=sqrt(kTC)
With reference to FIG. 1, if the effective capacitance associated with the charge store is, for example, 2.4 femto-Farads (fF), then the noise associated with resetting of the voltage level can be of order 20 electrons. Especially under low light conditions, this can be a dominant source of noise, since photon shot noise under low light is negligible, and image sensor circuits are designed to minimize all other sources of noise.